Disassembly - Voigtlander 28mm F2 Ultron II Type 2 Vintage Line - Leica M mount lens

 This article is focused on DIY repair of Voigtlander 28mm F2 Ultron II type 2 lens in Leica M mount.

The lens copy is provided by fredmiranda forum member Seabassius (thank you!) who discovered significant fragility of Voigtlander 28mm F2 lens by accidentally breaking it while simply dismounting lens hood. Yeah it may sound unusual, but with closer analysis of my lens copy of Voigtlander 28mm F2 I see how easy it is to damage lens that way if not paying attention.

I'm going to elaborate more on discovered weak spot of modern ultra compact Voigtlander lenses, because it may happen to few other modern Voigtlander lenses models, so it's important to know what NOT to do to keep your lens in a good mechanical order.

Fragility exploration

Personally I'm not a big fan of using lens hoods and often admiring optical impact of the side stray light on the photography rendering. I also prefer to keep lens size as small as possible. So at first glance I should never encounter situation of breaking Voigtlander lens when dismounting hood, right? Right?

No, in fact there is another scenario - using lens filters. In some cases lens filter may get stuck in front mount and removing it may require significant twisting effort, which may also lead to damaging lens focusing internals.

So what is actually happening, and where is the lens fragility? Problem origin is found, thanks to the experience shared by Seabassius on forum and deeper analysis of provided broken lens copy. It is coincidental set of following three conditions:

1. Two inner focusing helicoid guiders of Voigtlander 28mm F2 Ultron II lens are made of 1mm thick brass plates that have "U" shaped design for precise calibration.
2. Voigtlander 28mm F2 II lens body is very compact, it's not possible to grab the front area when removing hood.
3. It's easy to forget that lens hood need to be pushed first toward the lens then twisted for dismounting.

These brass braces are quite durable but are not unbreakable, and that durability is noticeably reduced by "U" shape design of the guiding plate with muddle cut area. Cross cut area of monolithic brass guider typically would be 1x4mm, but with that "U" shape design cross cut area is only about 1x2mm making guiders twice less resistant to side impact.

If you grab lens mount with one hand, and lens hood with other to twist - rotational power is directly stressing focus helicoid guiders (even when you are removing hood in easy way by first pushing toward lens). Same happens when hood is mounted on, or when attaching/detaching lens filters.

Good news is - the rotational force should be quite significant to bend or break the brass guiders, in most cases you'll not do that intentionally. However it is still possible, which will end in lens dismounted into two pieces. Same fragility exists in at least two other ultra-compact Voigtlander lenses - 21mm F3.5 and 35mm F2.

Disassembly and repair

Successful lens repair is requiring complete replacement of both brass guiders of focusing helicoid. It is not sort of parts you can purchase separately so replacement need to be DIY crafted. I'll show details of that process.

First I'm opening lens to get close access to focusing mechanics. The Voigtlander 28mm F2 Ultron II type 2 lens has exactly same internals and disassembly steps as type 1 version. Aperture need to be set to F2, then I'm removing retention ring and taking out front nameplate.

Then I'm unscrewing three black bolts sitting most deep, and detaching optical frame from focusing frame.

Next I'm unscrewing four black bolts and taking out remains of brass helicoid guiders (marked with red arrows below). You can see breakage areas on the edges, the surface area is very small there.

Important note on helicoid assembly (green arrows) - lens frame should be focused at infinity, and bolt socket should be located near 4ft mark when inner helicoid cylinder is screwed into it's thread.

Inner helicoid cylinder need to be unscrewed for cleaning off the old grease and possible metal dust remains in it from the guiders breakage. The helicoid guider slot is 4mm wide (green arrow below). I've made two guider replacements and made them solid for extra durability. I'm using Polar Bear Ultra-Soft grease for inner helicoid thread.

To screw in inner helicoid cylinder yo need to match thread when bolt socket is near "8" of "28" sign on lens frame focused to infinity. At that position the inner cylinder should protrude by about 2mm above fame edge.

Turn inner cylinder in CW direction until bolt socket is near 4ft mark. That will be correct position to put in helicoid guiders.

Screw in four black bolts but not tight yet. It is important to move focus ring and check that focus rotation is requiring minimal effort. Both guiders need to be slightly centered for that smooth focus movement to remain, only then tighten bolts and check that focus mechanics rotation remains smooth and effort is not increased, other wise loosen and reposition guiders.

DIY crafting of brass guiders

Here's approximate drawing of flat brass piece for helicoid guider and rough cut plate of brass. I'm using iron needle to mark drilling locations.

Brass part is put into wise and drilling is done.

Next step is to grind the part to proper width, which just a slightly more narrow than 4mm, and finally bending it to L shape.

At this point guider needs a bit of edges polishing effort and then ready to be mounted into the lens. If shape is moving too loose inside helicoid groove, brass edge can be accurately pressed to slightly expand.

Conclusions

I personally think that the chance of breaking Voigtlander lens helicoid is very low and would not worry at all about potential fragile areas of the lens since they still have great durability for normal lens use. However there are potential situations when you may accidentally put too much twisting force and damage or break the helicoid guiders. In that case most realistic scenario is to send lens to repair, and maintenance effort is relatively low if you have guiders replacement.

DIY crafting of replacement parts in solid design is requiring more noticeable effort and precise measurements and parts geometry tuning. It allows to bring lens mechanics to its original fully functional conditions with smooth focus operation, and introducing extra level of durability as a bonus. It is something was fun to work on, but is not something I'd gladly repeat again without having access to more advanced metal craft tools.

Does it make me look at Voigtlander Vintage Line lens durability from another angle? Definitely not, I still think that lens design is very durable and mechanics should last for decades if properly operated and maintained. I'm shooting with primarily Cosina Voigtlander lenses because they are always reliable for my personal use scenarios, in many cases easily DIY serviceable, have great manual focusing and optical rendering. It's just important to know strong and weak spots of your photo equipment and interact with it in optimal way, then results will be always very satisfying.